The present invention relates to xe2x80x9cactive implantable medical devicesxe2x80x9d as defined by the Jun. 20, 1990 Directive 90/385/CEE of the Council of the European Communities, more particularly to pacemaker devices including xe2x80x9cmultisitexe2x80x9d devices (triple or quadruple chamber), defibrillators and/or cardiovertors, which deliver to the heart low energy pulses for the treatment of heartbeat rate disorders.
Implantable devices are known which include stimulation circuits having automatic operation mode switching (xe2x80x9cAMSxe2x80x9d), as described, for example, in the EP-A-0 488 904 and its counterpart, U.S. Pat. No. 5,318,594, which are assigned to the assignee hereof, ELA Medical, Montrouge, France. More specifically, these devices, which include means for stimulation and detection of the atrium and the ventricle, can operate in one of two modes, for example, DDD and AAI (the AAI mode being a DDD mode including a lengthened atrio-ventricular delay interval), with automatic switching from one mode to the other.
The basic operating mode is typically an AAI mode, with a single chamber atrial simulation. The AAI mode is maintained as long as the atrio-ventricular conduction is normal, i.e., as long as each atrial event (either an atrial detection, corresponding to a spontaneous cardiac activity, or an atrial stimulation) is followed by an associated ventricular detection.
In certain circumstances, for example, during episodes of effort by the patient, atrio-ventricular blocks (xe2x80x9cAVBxe2x80x9d) can appear. These are known as xe2x80x9cparoxystic eventsxe2x80x9d, involving a depolarization defect of the ventricle. The paroxystic AVB can, however, intervene in circumstances other than those of a patient effort. In these cases, the pacemaker switches automatically into a DDD operating mode with parameters that are optimized for the temporary AVB condition.
To facilitate the return of a spontaneous atrio-ventricular conduction, the pacemaker DDD mode applies a relatively long atrio-ventricular delay (AVD). The AVD length is selected to allow for the patient""s spontaneous atrio-ventricular conduction to occur before a stimulation event is applied.
After the disappearance of the AVB condition, and thus re-establishment of a spontaneous AV (atrio-ventricular) conduction, the pacemaker returns automatically to its AAI operating mode once a certain number of known corresponding conditions have been fulfilled, as discussed, e.g., in U.S. Pat. No. 5,318,594.
It has now been discovered that the procedure described above is not well adapted to all types of AVB. Indeed, the switching into a DDD mode with a relatively long AVD, which seeks to support spontaneous AV conduction, is well adapted to a xe2x80x9cparoxysticxe2x80x9d type AVB, i.e., AVB started by an effort or other external cause, but which condition is temporary in duration. On the other hand, when a patient is subject to a chronic AVB condition, i.e., an AVB that persists over a period of several days, he or she will be stimulated continuously with a long AVD.
However, in this latter circumstance, lengthening of the AVD is not necessary, because it is useless to seek to support a spontaneous AV conduction, as such a spontaneous AV conduction will not likely be expressed. On the other hand, the lengthening of the AVD is potentially harmful because, when in a state of permanent stimulation, the optimal AVD are generally shorter than the spontaneous PR intervals (intervals between an atrial detection P and a ventricular detection R) of patients.
The present invention has for an object to resolve the problems set out above, and improve the operation of the known automatic mode switching implantable active medical devices in the case of AVB conditions.
The present invention is directed to use with a device having an automatic DDD/AAI mode switching as described in EP-A-0 488 904, and U.S. Pat. No. 5,318,594, which includes means for sensing spontaneous atrial and ventricular events; means for detecting an atrio-ventricular block condition preventing spontaneous atrio-ventricular conduction, and means for stimulating the atrium and the ventricle, the ventricular stimulation being applied on the detection of an atrio-ventricular block, after the completion of a programmed atrio-ventricular delay started on a spontaneous or stimulated atrial event.
According to the invention, this device also includes means for discriminating between a paroxystic and a chronic character of an atrio-ventricular block.
In one embodiment, the device additionally advantageously includes means for deactivating the automatic mode switching in the event of a determined chronic atrio-ventricular block, and automatically switching the device into a DDD operating mode and reprogramming the atrio-ventricular delay to have a value shorter than the previously programmed value in this DDD mode.
Preferably, the means for discriminating includes means for determining, in a first phase, a suspicion of a chronic atrio-ventricular block condition, and means, for confirming, in second phase, the presence of a chronic atrio-ventricular block in the event of consecutive suspected chronic atrio-ventricular blocks existing for a predetermined time.
In one embodiment, the first phase can be implemented at preset intervals, e.g., daily, and the second phase can be implemented over an interval of several days, optimally over a three-day interval. Thus, in one embodiment, three consecutive days of a suspected chronic AVB condition yields a confirmed AVB condition.
One criterion of suspicion of a chronic atrio-ventricular block that can be used by the discriminating means is the absence of a spontaneous AV conduction during the aforementioned predetermined period, or the absence of a spontaneous conduction after a predetermined number of determined spontaneous conductions, for example, approximately 500 conductions, detected on a daily basis.
A criterion of suspicion of a chronic atrio-ventricular block also can be the application, during the aforementioned predetermined period, of a number, or a percentage, of ventricular stimulation events over a number of cardiac cycles that is higher than a predetermined value, for example, a ventricular stimulation occurring more than 75% of the time, with an atrio-ventricular delay of a duration greater than a certain predetermined value, for example, greater than 200 ms. Other suitable criterion could be used.